1. Field of the Invention
The present invention relates to a semiconductor device and in particular, to a semiconductor device of BGA (ball grid array) configuration having a semiconductor ball as a semiconductor element I/O terminal.
2. Description of the Related Art
Conventional examples are shown in FIG. 5(A) and FIG. 5(B). The conventional examples shown here show a part of the BGA configuration of a semiconductor device using a BGA package.
The conventional example shown in FIG. 5(A) includes a solder ball 803 mounted on a land metal 802 arranged at a predetermined position on a package substrate (circuit substrate) 801. An IC including a semiconductor element is also arranged on the package substrate 801. The land metal 802 is arranged on the package substrate 801 as a signal I/O circuit with outside for the semiconductor element.
In this case, the solder ball 803, as shown in FIG. 5(A), is surrounded by a solder resist 805 and fixed to the land metal 802. The solder ball 803 is fixed to the land metal 802 by heat or conductive adhesive.
However, in this method, the solder ball 803 is attached to the land metal 802 through a surface contact, which does not provide a sufficient mechanical strength. In a fall test, a partial peel off may occur at a boundary 802a between the solder ball 803 and the land metal 802. Thus, it is difficult to realize a sufficient mounting strength.
In order to improve this situation, a technique as shown in FIG. 5(B) has been developed. That is, a solder ball 903 is mounted in such a manner that a land metal 902 protrudes into the solder ball 903. Here, a reference symbol 901 denotes a package substrate and a reference symbol 905 denotes a solder resist.
Moreover, Japanese Patent Publication 10-154766 [1] discloses another technique for increasing the bonding strength between the solder ball and the land metal. That is, a mechanical indentation is formed on the land metal so that the solder ball is attached into this indentation. This technique increases the contact area between the solder ball and the land metal, thereby increasing the bondage strength.
Furthermore, Japanese Patent Publication 8-274211 [2] discloses a technique in which an indentation is arranged at the center portion of the land metal and a mechanical groove is arranged on the land metal to communicate with the indentation, so that a contact surface of the solder ball in a deformed state is fixed into this indentation.
However, in the improved conventional example shown in FIG. 5(B), although the mechanical strength between the solder ball 903 and the land metal 902 is increased, the contact area between the land metal 902 and the package substrate 901 is decreased and the configuration does not allow the solder resist 905 to fix the land metal 902. Accordingly, no strength improvement can be observed in the fall test.
On the other hand, the boundary 902a between the land metal 902 and the package substrate 905 has a small contact area, easily causing a peel-off. Thus, the conventional example shown in FIG. 5(B) cannot realize a sufficient mounting strength.
Moreover, in the technique disclosed in Document [1] in which the solder ball is attached to a mechanical indentation, when attaching the solder ball air and excessive flux are easily contained in the indentation which is simply formed on the land metal. Air bubbles (voids) are generated on the bonding surface between the solder ball and the land metal, which lowers the bonding strength.
Furthermore, in the technique disclosed in Document [2], a mechanical indentation is formed together with a mechanical groove to communicate with the indentation on the land metal so that the solder ball is attached into the indentation. Since the solder ball is attached to the land metal in such a state that the contact surface of the solder ball is melted by heat, the melted contact surface may cover the groove at a timing slightly preceding attachment of the solder ball. This results in that air bubbles (voids) in the indentation remains at the contact surface with the solder ball or in the solder ball, which significantly weakens the solder ball strength at that portion and deteriorates the durability.
It is therefore an object of the present invention to provide a semiconductor device of the BGA configuration capable of maintaining a sufficient bondage strength between the land metal and the package substrate while increasing the mounting strength of the solder ball on the land metal, thereby realizing a sufficient durability.
In order to achieve the aforementioned object, the present invention provides a semiconductor device of the BGA configuration comprising: a circuit substrate; a wiring layer arrange on the circuit substrate via an insulation layer; a land metal portion formed on a part of the wiring layer; a solder resist layered so as to cover the land metal excluding a center portion thereof and the entire surface of the circuit substrate; and a solder ball arranged at the center portion of the land metal portion defined and surrounded by the solder resist;
wherein the land metal portion has a solder ball contact surface having a groove extending for continuous communication.
Accordingly, when mounting a solder ball 5, firstly a part of the solder ball 5 is pushed into the center portion of the groove formed on the land metal portion. Then, a part surrounding that part of the solder ball 5 is successively pushed into the groove. This increases the contact area between the solder ball and the land metal portion. This reduces the electric resistance when transmitting/receiving a signal, thereby reducing the signal attenuation.
Moreover, even when the solder ball is subjected to an external irregular pressing force in the lateral direction, the solder ball partially protruding into the groove has a strong mechanical strength can stand such a force. Thus, the bondage strength is increased and the mounting strength is significantly reinforced.
Here, the groove on the land metal portion may pass through the center portion of the solder ball contact surface. Moreover, the groove is preferably realized by two line-shaped grooves. In this case, the line-shaped grooves may intersect each other at the center portions thereof.
In this case, the contact area between the solder ball and the land metal portion is increased according to the state of the groove, increasing the solder ball mounting strength.
Furthermore, an air exhaust groove may be arranged for each end of the groove in a solder resist portion covering the ends of the groove so that each end of the groove communicates with the external atmosphere. In this case, the air exhaust groove may communicate each end of the groove directly with the external atmosphere without spreading around the groove.
This facilitates exhaust of remaining flux as an adhesive and remaining air as a result after the solder ball is mounted. That is, even if air and the like are enclosed in the groove by the solder ball, the air is pushed out through the groove into the air exhaust groove and then outside.
According to another aspect of the present invention, there is provided a semiconductor device of the BGA configuration comprising: a circuit substrate; a wiring layer arrange on the circuit substrate via an insulation layer; a land metal portion formed on a part of the wiring layer; a solder resist layered so as to cover the land metal excluding a center portion thereof and the entire surface of the circuit substrate; and a solder ball arranged at the center portion of the land metal portion defined and surrounded by the solder resist;
wherein the land metal portion has a solder ball contact surface having a line-shaped protrusion extending continuously.
This also enables to obtain a semiconductor device having an increased mounting strength functioning almost in the same way as the case when the aforementioned groove is arranged.
Here, the line-shaped protrusion may pass through the center portion of the solder ball contact surface. Moreover, the line-shaped protrusion preferably consists of at least two line-shaped protrusions. Furthermore, the two line-shaped protrusions may intersect each other at the center portion thereof.
In this case also, the contact area between the solder ball and the land metal portion is increased according to the state of the line-shaped protrusion(s), thereby increasing the solder ball mounting strength.
Furthermore, a predetermined air exhaust groove may. be provided at a side wall of the solder resist covering the circumference of the land metal so that a circumferential portion of the solder resist can communicates with the external atmosphere.
This facilitates exhaust of remaining flux as an adhesive and remaining air after the solder ball is mounted. That is, even when remaining air and the like are enclosed over the land metal portion by the solder ball, the remaining air and the like are pushed from the end portion of the land metal portion into the air exhaust groove and then outside.